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Date: Thu, 25 Apr 2019 13:44:24 +0000
From: "liucheng (G)" <liucheng32@...wei.com>
To: "musl@...ts.openwall.com" <musl@...ts.openwall.com>
CC: "liucheng (G)" <liucheng32@...wei.com>
Subject: [patch] return value of ulimit(UL_GETFSIZE) in X32 architecture

Dear ALL,

Return value of ulimit(UL_GETFSIZE) in X32 architecture seems to be wrong.

Here is the implementation of ulimit function in MUSL 1.1.22:
#include <sys/resource.h>
#include <ulimit.h>
#include <stdarg.h>

long ulimit(int cmd, ...)
{
                 struct rlimit rl;
                 getrlimit(RLIMIT_FSIZE, &rl);
                 if (cmd == UL_SETFSIZE) {
                         long val;
                         va_list ap;
                         va_start(ap, cmd);
                         val = va_arg(ap, long);
                         va_end(ap);
                         rl.rlim_cur = 512ULL * val;
                                     if (setrlimit(RLIMIT_FSIZE, &rl)) return -1;
                 }
                 return rl.rlim_cur / 512;
}

Make it simple in case of "cmd = UL_GETFSIZE", ulimit function becomes to be:
         long ulimit(int cmd, ...)
         {
                   struct rlimit rl;
                   getrlimit(RLIMIT_FSIZE, &rl);
                   return rl.rlim_cur / 512;
}

rl.rlim in ulimit function is the type of long long(8 Byte), however the return value in X32 architecture is the type of long(4 Byte).
So in that case, rl.rlim_cur / 512 would be larger than 0x7fffffff and ulimit function returns -1.


I also tried an experiment to improve my opinion as follows.

[benchmark]
$ cat ulimit_test.c
#include <stdio.h>
#include <ulimit.h>

int main()
{
        printf("ret:%d\n", ulimit(UL_GETFSIZE));

        return 0;
}

[testcase]
Environment: Linux 4.4.171 #1 SMP Thu Apr 25 00:39:22 UTC 2019 armv7l GNU/Linux

$ /tmp # ulimit -f
unlimited
$ /tmp # ./ulimit_test
ret:-1
$ /tmp # cp musl/libc.so /usr/lib/                                 // copy a new MUSL libc.so with my [patch]
$ /tmp # ./ulimit_test
ret:2147483647                                                               // 0x7fffffff

[patch]
---
diff --git a/src/legacy/ulimit.c b/src/legacy/ulimit.c
index 1f59e8e..d1620e6 100644
--- a/src/legacy/ulimit.c
+++ b/src/legacy/ulimit.c
@@ -1,6 +1,7 @@
#include <sys/resource.h>
#include <ulimit.h>
#include <stdarg.h>
+#include <limits.h>
 long ulimit(int cmd, ...)
{
@@ -15,5 +16,5 @@ long ulimit(int cmd, ...)
                rl.rlim_cur = 512ULL * val;
                if (setrlimit(RLIMIT_FSIZE, &rl)) return -1;
       }
-        return rl.rlim_cur / 512;
+       return rl.rlim_cur == RLIM_INFINITY ? LONG_MAX : rl.rlim_cur / 512;
}
---

Looking forward to your reply.
Best regards.
Cheng Liu


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